Good morning and welcome to "this week." White house in crisis. I knew this was going to be a heavy lift. Obama's high stakes syria gamble failing fast. Can he salvage a win? Can his presidency survive a defeat? What will it mean for america's security and our role in the world? This morning, breaking details from syria from the white house, congress, and our powerhouse roundtable. Plus. Does the state department know you're speaking out now? No, they don't know I'm here. One year after benghazi, the first interview with the senior diplomat on the ground. The inside story of the attack. And a congresswoman's miracle baby. How she beat the odds against a fatal disease. That is her personality. She's such a fighter. All that right here this sunday morning. Hello again. It wasn't on the agenda one month ago, but now the vote to use military force in syria has become the most critical test of the obama presidency. The stakes are high. America's security and credibility on the line. So is the balance of power between the president and congress, and the rest of the agenda in the second term. Right now it's a vote the president would lose. Abc's whip count in the house shows 229 members likely in the no camp, only 44 are likely to vote question are. And more on that from abc news white house correspondent john karl. The situation a bit better in the senate. This is an uphill battle for the white house, and they know it. Reporter: That's right. Even white house officials acknowledge if the vote were today, the president would lose. But they are promising a massive effort to turn that around. This is the biggest congressional effort by the white house since the battle over health care in the first year as president. It's a visible effort. First the president doing six network television interviews, national interviews tomorrow. There'll be a big address to the nation on tuesday. And, george, the most interesting thing, they have enlisted former members of the bush administration to make the case for republicans. Including bush's former national security adviser steven hadley who's talking directly to republican members of congress. But the president is making a personal effort. Individual members to the white house and into the situation room to show classified evidence. One key thing that is not happening here, the president's grassroots army, organizing for america, 30 million twitter followers, they are on the sidelines. They will not be taking part. Not a lot of support from the president's base. But what if he can't turn this around? The white house is dancing over that question. Reporter: That's the big question, especially with the vote count. I tried to ask that to the president, he told me point blank he would not give me a direct answer. But what I can say, some of his top advisers say they cannot conceive of him going forward if congress says no. On the other hand, we've had military officials tell us given where the planning is, they can't see pulling the plug either. Thanks very much. Right to the president's chief OF STAFF, denis McDonough. So many questions about the president and what he would do. If he can't succeed in the getting the votes in the next couple of weeks. As john pointed out, the president did not directly answer the question on friday. But he said his call to congress was not a political ploy or symbolism. And he went on to say this. I put it before congress because I could not honestly claim that the threat posed by assad's use of chemical weapons posed an imminent, direct threat to the united states. With those words, hasn't the president effectively ruled out taking any action if the congress votes no? George, I think it's important for us to -- before we jump to conclusions, I admire john karl's reporting, but look, I've been talking to dozens of members of congress over the last week. Not a single one has rebut order refused the intelligence. Which is to say everybody agrees THAT ON AUGUST 21st, ASSAD USED Chemical weapons against his own people. So the question for congress this week is a very simple one. Should there be consequences for his having used gases, chemical weapons, to kill more than a thousand of his own people, including more than 400 children? The answer to that question will be followed closely in tehran. The answer will be followed closely in damascus, followed very closely by members of lebanese hezbollah. This is a big question and big week to address that for congress, the fundamental national security issue. As the president said, we didn't go to congress because we thought this was an empty exercise. We are investing a lot of time and effort in this because we think congress should be a full partner in our national security matters, and when they are, we're stronger as a country. Members of congress need to understand that if they want to see assad held to account for this activity, they should vote yes on the resolution. I understand that's the argument, but members of congress aren't buying in, at least not yet. And some have raised the specter of impeachment if the president goes forward in the absence of congressional approval. Here's duncan hunter, republican of california. I think he's breaking the law if he strikes without congressional approval and if he proceeds without congress providing that authority, it should be considered an impeachable offense. How will the president factor that into his final decision? The president is focused on right now, george, is the national security implications of what is undeniably and un-rebutted intelligence which suggests that the assad regime use chemical weapons against its own people, killing 400 children. That's what he's focused on right now. We believe that we have the capability in place to do it. Congress should be the full partner in the effort. That's what we're focused on. That's the question before congress this week. My hunch is you know washington better than anybody, george. There'll be all sorts of distractions and other things that try to knock us off our game. But that's the question before us and congress this week. I know you're not going to give a yes or no on answer on what the president would do if they don't vote for it. But what are the consequences. You have hinted at some of them. What are the consequences if the president and congress can't go forward after this? How much damage will that do to the presidency. Ross of the new york times and many others have said this would finish off the president as a credible actor on the world stage. Do you agree? I really enjoy ross's reporting and writing, he's thoughtful. I have to say that right now politics, all those questions, are going to be debated and worked out by others. We're focused on the national security question before us. It's a fundamental and important question. Will there be consequences? Now, what we're trying to reinforce here and what our allies supported us, reinforcing at the g-20 on friday is a prohibition that goes back a hundred years against chemical weapons. Why does that matter? In world war i, the troops were subject to chemical weapons attack regularly. Not since world war I has it seen the same kinds of attacks. That's important, increases security, reduces the burden against our men and women in the armed forces, who are taking a lot of burdens, by the way. We to want underscore this and think congress should join us in doing it. Facing a lot of opposition. Moveon.Org, strong support of the president backed him up on the opposition to the iraq war. But this new ad exclusively they have given us this new ad they're going to start running tomorrow. Take a look. He never set out to spend eight years at war in iraq, or to be mired from a decade of fighting in afghanistan. What should america expect if we rush into syria, alone, with no real plan for the consequences? We already know. It gets worse. Meanwhile, senator ted cruz, republican of texas, said they would be serving as al-qaeda's air force. You're seeing opposition from both the left and the right, your response? I'm outraged for somebody to suggest our people would be serving as allies to al-qaeda. One. Two, on the question of what this is and isn't. What this is, george, very clear. Targeted, consequential, limited attack against assad forces. And assad capabilities so that he is deterred from carrying out these actions again. Here is what it is not. It's not boots on the ground, extended air campaign, not iraq, afghanistan, or libya. This is a very concerted, concentrated, limited effort that we can carry out and that can underscore and secure our interests. Finally, yes or no question, will the resolution pass? This resolution is going to pass after we work this this week. Members have been in the districts and states. We have been talking to many of them, dozens of them. When they see the intelligence, they don't rebut it. The bottom line is, they have to answer the question. Should there be consequences? And the answer will be followed closely in tehran, in damascus and elsewhere. denis McDonough, thank you very much.

This transcript has been automatically generated and may not be 100% accurate.

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